Laser spark plug

ABSTRACT

A laser spark plug device for an internal combustion engine includes a prechamber for receiving an ignitable medium and at least one overflow channel providing a fluid connection between an internal space of the prechamber and an external space surrounding the prechamber. The at least one overflow channel is configured such that when a fluid flows through the overflow channel into the internal space of the prechamber, the result is a fluid flow having at least one eddy which rotates on an eddy axis forming an angle of more than approximately 45° with a longitudinal axis of the laser spark plug device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a laser spark plug for an internalcombustion engine, the laser spark plug having a prechamber forreceiving an ignitable medium and at least one overflow channel makingpossible a fluid connection between one internal space of the prechamberand one external space surrounding the prechamber.

2. Brief Summary of the Invention

An object of the present invention is to provide an improved laser sparkplug of the type referred to at the outset for the purpose of ensuringreliable operation and longer life.

This objective is achieved in a laser spark plug of the type referred toat the outset in that the at least one overflow channel is situated anddesigned in such a way that when a fluid flows through the overflowchannel into the internal space of the prechamber, the result is a fluidflow having at least one eddy which rotates on an eddy axis forming anangle of more than approximately 45° to a longitudinal axis of the laserspark plug.

It is particularly preferred that the at least one overflow channel issituated outside of the longitudinal axis.

According to the present invention, it has been recognized that such afluid flow contributes favorably to preventing stagnation flows in thearea of a surface of a combustion chamber window of the laser sparkplug. Consequently, oil ashes or other particles arising duringcombustion in the prechamber accumulate to only a slight degree on thesurface of the combustion chamber window, thus ensuring more reliablelaser ignition and longer life than is the case in the conventionallaser ignition systems having a prechamber.

In an example embodiment of the laser spark plug according to thepresent invention, the angle between the eddy axis and the longitudinalaxis of the laser spark plug is between approximately 80° andapproximately 90°, preferably approximately 90°. A fluid flow satisfyingan angle condition of this type in relation to the longitudinal axis ofthe laser spark plug is also denoted as a so-called tumble flow.

The design of a tumble flow achieved according to the present inventionmakes it possible in a particularly advantageous manner to protect asurface of the combustion chamber window of the laser spark plug againstthe accumulation of combustion products, since it strongly reduces oreliminates a normal component of the flow velocity directed to thecombustion chamber window.

According to another variant of the invention, the design of a tumbleflow according to the present invention is favored in that the at leastone overflow channel is situated in such a way that its longitudinalaxis in the radial direction forms an angle with the longitudinal axisof the laser spark plug which is smaller than approximately 25°,preferably smaller than approximately 10°.

According to another example embodiment, it is particularly preferredthat a plurality of overflow channels are provided, the longitudinalaxes of adjacent overflow channels forming a maximum angle of 20°,preferably a maximum angle of 10°.

This variant of the present invention is preferred in such overflowchannels, the orifices of which are situated in a face-side area of theprechamber facing the combustion chamber.

Another variant of the present invention results in a particularlyintensive fluid flow according to the present invention when a pluralityof overflow channels are provided which are situated and designed insuch a way that the longitudinal axes of at least three overflowchannels intersect at a point of intersection lying in the internalspace of the prechamber. The addition of the partial flows flowingthrough the individual overflow channels favors the formation of aparticularly strong fluid flow in the sense of a tumble flow.

A tumble flow in the prechamber may be achieved further in aparticularly reliable manner in that the point of intersection lies in aradially external area of the prechamber, the point of intersectionbeing at a distance of at least 50% to approximately 70% of a radius ofthe prechamber from the longitudinal axis of the laser spark plug or theprechamber.

According to another variant of the present invention, distribution ofignition flares emerging from the prechamber that is as uniform aspossible as necessary for efficient ignition is ensured, if openingsopening into the external space of the overflow channels, whoselongitudinal axes intersect in the internal space of the prechamber, aresubstantially at a uniform distance from one another and/or thelongitudinal axis of the laser spark plug, in particular in the area ofthe corners of a fictional n-corner, n being ≧3.

According to another advantageous variant of the present invention, atleast one flow-guiding element may be provided which is designed forsupporting the fluid flow and in particular for guiding the flowtangentially past a surface of a combustion chamber window facing theprechamber. To that end, the at least one flow-guiding element may havea flow-guiding surface, the shape of which roughly corresponds to anexternal contour of a tumble flow or an associated eddy which is seen asideal.

According to another advantageous variant of the present invention, anoptimal design of such a tumble flow is favored in that a combustionchamber window is provided and situated in such a way that its surfacefacing the prechamber is flush with one internal wall of the prechamberat least sectionally.

According to another variant of the present invention, an optimalimplementation of the ignitable mixture located in the prechamberresults when the laser spark plug is designed for radiating laserradiation onto an ignition point lying in the prechamber, the distanceof which from a combustion chamber window is less than its distance froman end area of the prechamber facing the combustion chamber, inparticular by at least approximately 50% less. This advantageously hasthe result that the flame core arising in the ignition point duringlaser ignition is carried along by the tumble flow produced according tothe present invention and is guided into an end area of the prechamberfacing the combustion chamber. The further development of a flame frontin this area has the particular advantage that less unburned mixture isdischarged from the prechamber into the external space or combustionchamber, resulting in increased efficiency of laser ignition in theprechamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a partial cross-section of a first example embodiment of alaser spark plug according to the present invention.

FIG. 2 shows another example embodiment of the laser spark plugaccording to the present invention having optimized flow guidance in aboundary area between the combustion chamber window and the internalwall of the prechamber.

FIGS. 3 a and 3 b show additional variants of a laser spark plugaccording to the present invention.

FIG. 4 shows a front view of an end of another example embodiment of thelaser spark plug according to the present invention facing thecombustion chamber.

FIG. 5 shows a perspective view of an end area of another exampleembodiment of the laser spark plug according to the present inventionfacing the combustion chamber.

FIGS. 6 a through 6 d show various operating phases of the laser sparkplug according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a partial cross section of a first example embodiment oflaser spark plug 100 according to the present invention. Laser sparkplug 100 has an integrated laser device 105 which is able to generatelaser radiation 20 and bundle it onto ignition point ZP lying in aprechamber 110 of laser spark plug 100.

The internal space of prechamber 110 is separated from part 100 a oflaser spark plug 100 facing away from the combustion chamber by acombustion chamber window 140.

Furthermore, laser spark plug 100 or its prechamber 110 has overflowchannels 120 which make a fluid connection possible between prechamber110 and an external area 200, which may be, for example, a combustionchamber of the internal combustion engine when laser spark plug 100 isinstalled in an internal combustion engine.

According to the present invention, at least one overflow channel 120 issituated and designed in such a way that when a fluid flows throughoverflow channel 120 into internal space 111 of prechamber 110, theresult is a fluid flow F having at least one eddy which rotates on aneddy axis WA forming an angle of more than approximately 45° with alongitudinal axis LA of laser spark plug 100.

It is particularly preferred that overflow channel 120 is situatedoutside of longitudinal axis LA, which further favors the formation offluid flow F according to the present invention.

In the present case, the fluid flow formed according to the presentinvention is denoted by block arrow F. A corresponding eddy axis isperpendicular to the plane of projection in FIG. 1. In the present caseeddy axis WA accordingly forms a right angle with longitudinal axis LAof laser spark plug 100. In this case, fluid flow F provided accordingto the present invention is also described as a so-called tumble flow.

Tumble flow F advantageously has only one tangential flow velocitycomponent in relation to surface 140 a of combustion chamber window 140,advantageously preventing the deposition of combustion products onsurface 140 a.

For the further support of tumble flow F, at least one flow-guidingelement 130 may also be provided in prechamber 110.

According to another particularly preferred variant of the presentinvention, at least one overflow channel 120 is situated in such a waythat its longitudinal axis KLA in relation to longitudinal axis LA oflaser spark plug 100 in the radial direction forms an angle β withlongitudinal axis LA of laser spark plug 100 which is smaller thanapproximately 25°, preferably smaller than approximately 10°.

According to another example embodiment of the present invention, it mayalso be provided that a plurality of overflow channels 120 are orientedin such a way that the longitudinal axes of adjacent overflow channelsform a maximum angle Y of 20°, preferably a maximum angle of 10°. Thisalso applies to an observation in relation to longitudinal axis LA in aradial and also in an axial direction.

FIG. 2 shows a partial cross section of another example embodiment ofthe laser spark plug according to the present invention, prechamber 110already being formed in such a way that it ensures optimized flowguidance due to appropriately rounded internal wall sections 110 a. Inthis case, no separate flow-guiding element 130, see FIG. 1, isnecessary.

FIG. 3 a shows another example embodiment of a prechamber 110 accordingto the present invention, a combustion chamber window 140′ which has asubstantially T-shaped cross section being provided. This makes itpossible to improve the fit of combustion chamber window 140′ incorresponding receiving means, not described in greater detail here, oflaser spark plug 100. Furthermore, combustion chamber window 140′ mayalso be situated advantageously in relation to prechamber 110 in such away that a surface 140 a′ of combustion chamber window 140′ facingprechamber 110 is flush with an internal wall section 110 a ofprechamber 110.

FIG. 3 b shows another variant of a prechamber 110 for a laser sparkplug according to the present invention, in which combustion chamberwindow 140 is set back by a discrete distance in relation to internalspace 111 of prechamber 110, which also reduces an accumulation ofcombustion products on combustion chamber window 140.

FIG. 4 shows a front view of another example embodiment of a laser sparkplug according to the present invention, prechamber 110 having a totalof five overflow channels, of which only the openings opening intoexternal space 200 surrounding prechamber 110 are denoted as 120 a′, 120b′, 120 c′, 120 d′, 120 e′.

As shown in FIG. 4, a basically asymmetric positioning of the overflowchannels or their respective openings 120 a′, 120 b′, 120 c′, 120 d′,120 e′—in relation to longitudinal axis LA (FIG. 1)—in the direction ofexternal space 200 is also suitable for making a tumble flow accordingto the present invention possible.

FIG. 5 shows a perspective view of the laser spark plug according to thepresent invention, five overflow channels 120 a, 120 b, 120 c, 120 d,120 e also being provided in this case.

In this case, overflow channels 120 a, 120 b, 120 c, 120 d, 120 e aresituated and designed in such a way that the longitudinal axes of atleast three overflow channels 120 a, 120 c, 120 e intersect in internalspace 111 (FIG. 1) of prechamber 110, and specifically at a point ofintersection SP, as a result of which the individual partial flows areadvantageously added to one another to form a tumble flow F (FIG. 1).

A particularly efficient formation of a fluid flow F into the internalspace of prechamber 110 according to the present invention is ensured ifpoint of intersection SP lies in a radially external area of prechamber110, point of intersection SP in particular being at a distance ofapproximately 50% to approximately 70% of the radius of prechamber 110from longitudinal axis LA of laser spark plug 100.

According to another advantageous variant of the present invention,substantially uniform action on the external space or combustion chamber200 by ignition flares emerging from prechamber 110 is ensured, in thatopenings 120 a′, 120 c′, 120 e′ (FIG. 5) opening into external space 200of the overflow channels 120 a, 120 c, 120 e, whose longitudinal axesintersect in internal space 111 of prechamber 110, are substantially ata uniform distance from one another and/or from longitudinal axis LA oflaser spark plug 100, in particular in the area of the corners of afictional n-corner, n being ≧3.

If fluid flows out of external space 200 into internal space 111 ofprechamber 110, this configuration simultaneously favors an advantageousaddition of the partial flows of the three intersecting overflowchannels in such a way that an intensified fluid flow F according to thepresent invention is present at the outlet end in the area ofintersection of the overflow channels.

FIGS. 6 a to 6 d show various operating phases of a laser spark plug 100according to the present invention.

The design of laser spark plug 100 according to the present invention insuch a way that laser radiation 20 is radiated onto an ignition point ZPlying in prechamber 110, the distance d1 of which from a combustionchamber window 140 is smaller than its distance d2 from an end area 110a of prechamber 110 facing the combustion chamber, advantageously causesa flame core produced in ignition point ZP to be carried along by fluidflow F according to the present invention, which in the present caseresults in a clockwise movement of the flame core through internal space111 of prechamber 110, see FIGS. 6 b through 6 d.

After laser ignition, fluid flow F according to the present inventioncarries the flame core clockwise in the direction of end area 110 afacing the combustion chamber (FIG. 6 a) of prechamber 110, so that theflame subsequently ignites from there from the residual product of theprechamber volume. Compared to conventional prechambers without tumbleflow in which a flame front burns from one combustion chamber window inthe direction of end area 110 a facing the combustion chamber, lessunburned mixture is ejected from prechamber 110 into main combustionchamber 200 when the pressure in prechamber 110 rises due to theincipient combustion. When the principle according to the presentinvention is used, the prechamber volume is thus used more efficientlythan in conventional laser spark plugs.

This advantageously makes it possible to design the relevant components,in particular prechamber 110, to be smaller than in conventional systemswithout having to accept a loss of ignition performance in return.

Due to the asymmetric positioning of overflow channels 120 in severalexample embodiments of the laser spark plug according to the presentinvention, it may be necessary to assemble laser spark plug 100according to the present invention in a targeted manner in relation tothe cylinder head of the destination system.

The provision of curved overflow channels may advantageously contributeto directing ignition flares emerging from prechamber 110 intocombustion chamber 200 in a desired direction, in particulardistributing them uniformly in combustion chamber 200.

1. A laser spark plug device for an internal combustion engine,comprising: a prechamber configured to receive an ignitable medium; andat least one overflow channel situated outside of a longitudinal axis ofthe laser spark plug device and configured to provide a fluid connectionbetween an internal space of the prechamber and an external spacesurrounding the prechamber, wherein the at least one overflow channel isconfigured in such a way that when a fluid flows through the overflowchannel into the internal space of the prechamber a fluid flow having atleast one eddy is generated in the internal space of the prechamber, theat least one eddy rotating on an eddy axis forming an angle of more thanapproximately 45° with the longitudinal axis of the laser spark plugdevice; wherein the angle between the eddy axis and the longitudinalaxis of the laser spark plug device is between approximately 80° andapproximately 90°; and wherein a longitudinal axis of the at least oneoverflow channel forms an angle smaller than approximately 25° with thelongitudinal axis of the laser spark plug device.
 2. The laser sparkplug device as recited in claim 1, wherein a plurality of overflowchannels are provided, and wherein the longitudinal axes of adjacentoverflow channels form a maximum angle of 20°.
 3. The laser spark plugdevice as recited in claim 1, wherein a plurality of overflow channelsare provided, and wherein the longitudinal axes of at least threeoverflow channels intersect at a point of intersection located in theinternal space of the prechamber.
 4. The laser spark plug device asrecited in claim 3, wherein the point of intersection lies in a radiallyouter region of the internal space of the prechamber.
 5. The laser sparkplug device as recited in claim 3, wherein openings of the at leastthree overflow channels facing the external space surrounding theprechamber and having the longitudinal axes intersecting at the point ofintersection in the internal space of the prechamber are at least one of(i) at a substantially uniform distance from one another and (ii) at asubstantially uniform distance from the longitudinal axis of the laserspark plug device.
 6. The laser spark plug device as recited in claim 3,further comprising: a combustion chamber window having a surface facingthe prechamber; and at least one flow-guiding element configured toguide the fluid flow tangentially past the surface of the combustionchamber window facing the prechamber.
 7. The laser spark plug device asrecited in claim 3, further comprising: a combustion chamber windowhaving a surface facing the prechamber, wherein the surface facing theprechamber is flush with at least a portion of an internal wall of theprechamber.
 8. The laser spark plug device as recited in claim 3,further comprising: a combustion chamber window having a surface facingthe prechamber; wherein the laser spark plug device is configured toradiate laser radiation onto an ignition point lying in the prechamber,and wherein the distance of the ignition point from the combustionchamber window is at least approximately 50% less than the distance ofthe ignition point from an end area of the prechamber facing thecombustion chamber.